The HER protein family consists of 4 members: HER1, also named epidermal growth factor receptor (EGFR) or ErbB-1, HER2, also named ErbB-2, ErbB-3, also named HER3 and ErbB-4, also named HER4. The ErbB family proteins are receptor tyrosine kinases and represent important mediators of cell growth, differentiation and survival. The HER family represent receptor proteins of different ligands of the epidermal growth factor family (EGF-family) like epidermal growth factor (EGF), the neuregulin (NRG) family, amphiregulin, and transforming growth factor-α (TGF-α).
HER1 and Anti-HER1 Antibodies
Human HER1 ((also known as epidermal growth factor receptor EGFR or Erb-B1) is a 170 kDa transmembrane receptor encoded by the c-erbB proto-oncogene, and exhibits intrinsic tyrosine kinase activity (Modjtahedi, H., et al., Br. J. Cancer 73 (1996) 228-235; Herbst, R. S., and Shin, D. M., Cancer 94 (2002) 1593-1611). SwissProt database entry P00533 provides the sequence of HER1 (SEQ ID NO: 2). There are also isoforms and variants of HER1 (e.g., alternative RNA transcripts, truncated versions, polymorphisms, etc.) including but not limited to those identified by Swissprot database entry numbers P00533-1, P00533-2, P00533-3, and P00533-4. HER1 is known to bind ligands including α), epidermal growth factor (EGF), transforming growth factor-α (TGF), amphiregulin, heparin-binding EGF (hb-EGF), betacellulin, and epiregulin (Herbst, R. S., and Shin, D. M., Cancer 94 (2002) 1593-1611; Mendelsohn, J., and Baselga, J., Oncogene 19 (2000) 6550-6565). HER1 regulates numerous cellular processes via tyrosine-kinase mediated signal transduction pathways, including, but not limited to, activation of signal transduction pathways that control cell proliferation, differentiation, cell survival, apoptosis, angiogenesis, mitogenesis, and metastasis (Atalay, G., et al., Ann. Oncology 14 (2003) 1346-1363; Tsao, A. S., and Herbst, R. S., Signal 4 (2003) 4-9; Herbst, R. S., and Shin, D. M., Cancer 94 (2002) 1593-1611; Modjtahedi, H., et al., Br. J. Cancer 73 (1996) 228-235).
Unconjugated monoclonal antibodies (mAbs) can be useful medicines for the treatment of cancer, as demonstrated by the U.S. Food and Drug Administration's approval of Trastuzumab (Herceptin™; Genentech Inc) for the treatment of advanced breast cancer (Grillo-Lopez, A. J., et al., Semin. Oncol. 26 (1999) 66-73; Goldenberg, M. M., Clin. Ther. 21 (1999) 309-18), Rituximab (Rituxan™; IDEC Pharmaceuticals, San Diego, Calif., and Genentech Inc., San Francisco, Calif.), for the treatment of CD20 positive B-cell, low-grade or follicular Non-Hodgkin's lymphoma, Gemtuzumab (Mylotarg™, Celltech/Wyeth-Ayerst) for the treatment of relapsed acute myeloid leukemia, and Alemtuzumab (CAMPATH™, Millenium Pharmaceuticals/Schering AG) for the treatment of B cell chronic lymphocytic leukemia. The success of these products relies not only on their efficacy but also on their outstanding safety profiles (Grillo-Lopez, A. J., et al., Semin. Oncol. 26 (1999) 66-73; Goldenberg, M. M., Clin. Ther. 21 (1999) 309-18). In spite of the achievements of these drugs, there is currently a large interest in obtaining higher specific antibody activity than what is typically afforded by unconjugated mAb therapy.
The results of a number of studies suggest that Fc-receptor-dependent mechanisms contribute substantially to the action of cytotoxic antibodies against tumors and indicate that an optimal antibody against tumors would bind preferentially to activation Fc receptors and minimally to the inhibitory partner FcγRIIB (Clynes, R. A., et al., Nature Medicine 6(4) (2000) 443-446; Kalergis, A. M., and Ravetch, J. V., J. Exp. Med. 195(12) (2002) 1653-1659. For example, the results of at least one study suggest that polymorphism in the FcγRIIIa receptor, in particular, is strongly associated with the efficacy of antibody therapy. (Cartron, G., et al., Blood 99 (3) (2002) 754-758). That study showed that patients homozygous for FcγRIIIa have a better response to Rituximab than heterozygous patients. The authors concluded that the superior response was due to better in vivo binding of the antibody to FcγRIIIa, which resulted in better ADCC activity against lymphoma cells (Cartron, G., et al., Blood 99(3) (2002) 754-758).
Various strategies to target EGFR and block EGFR signaling pathways have been reported. Small-molecule tyrosine kinase inhibitors like gefitinib, erlotinib, and CI-1033 block autophosphorylation of EGFR in the intracellular tyrosine kinase region, thereby inhibiting downstream signaling events (Tsao, A. S., and Herbst, R. S., Signal 4 (2003) 4-9). Monoclonal antibodies, on the other hand, target the extracellular portion of EGFR, which results in blocking ligand binding and thereby inhibits downstream events such as cell proliferation (Tsao, A. S., and Herbst, R. S., Signal 4 (2003) 4-9).
Several murine monoclonal antibodies have been generated which achieve such a block in vitro and which have been evaluated for their ability to affect tumor growth in mouse xenograft models (Masui, H., et al., Cancer Res. 46 (1986) 5592-5598; Masui, H., et al., Cancer Res. 44 (1984) 1002-1007; Goldstein, N., et al., Clin. Cancer Res. 1 (1995) 1311-1318). For example, EMD 55900 (EMD Pharmaceuticals) is a murine anti-EGFR monoclonal antibody that was raised against human epidermoid carcinoma cell line A431 and was tested in clinical studies of patients with advanced squamous cell carcinoma of the larynx or hypopharynx (Bier, H., et al., Eur. Arch. Otohinolaryngol. 252 (1995) 433-9). In addition, the rat monoclonal antibodies ICR16, ICR62, and ICR80, which bind the extracellular domain of EGFR, have been shown to be effective at inhibiting the binding of EGF and TGF-α the receptor. (Modjtahedi, H., et al., Int. J. Cancer 75 (1998) 310-316). The murine monoclonal antibody 425 is another MAb that was raised against the human A431 carcinoma cell line and was found to bind to a polypeptide epitope on the external domain of the human epidermal growth factor receptor. (Murthy, U., et al., Arch. Biochem. Biophys. 252(2) (1987) 549-560. A potential problem with the use of murine antibodies in therapeutic treatments is that non-human monoclonal antibodies can be recognized by the human host as a foreign protein; therefore, repeated injections of such foreign antibodies can lead to the induction of immune responses leading to harmful hypersensitivity reactions. For murine-based monoclonal antibodies, this is often referred to as a Human Anti-Mouse Antibody response, or “HAMA” response, or a Human Anti-Rat Antibody, or “HARA” response. Additionally, these “foreign” antibodies can be attacked by the immune system of the host such that they are, in effect, neutralized before they reach their target site. Furthermore, non-human monoclonal antibodies (e.g., murine monoclonal antibodies) typically lack human effector functionality, i.e., they are unable to, inter alia, mediate complement dependent lysis or lyse human target cells through antibody dependent cellular toxicity or Fc-receptor mediated phagocytosis.
Chimeric antibodies comprising portions of antibodies from two or more different species (e.g., mouse and human) have been developed as an alternative to “conjugated” antibodies. For example, U.S. Pat. No. 5,891,996 (Mateo de Acosta del Rio, C. M., et al.) discusses a mouse/human chimeric antibody, R3, directed against EGFR, and U.S. Pat. No. 5,558,864 discusses generation of chimeric and humanized forms of the murine anti-EGFR MAb 425. Also, IMC-C225 (Erbitux®; ImClone) is a chimeric mouse/human anti-EGFR monoclonal antibody (based on mouse M225 monoclonal antibody, which resulted in HAMA responses in human clinical trials) that has been reported to demonstrate antitumor efficacy in various human xenograft models. (Herbst, R. S., and Shin, D. M., Cancer 94 (2002) 1593-1611). The efficacy of IMC-C225 has been attributed to several mechanisms, including inhibition of cell events regulated by EGFR signaling pathways, and possibly by increased antibody-dependent cellular toxicity (ADCC) activity (Herbst, R. S., and Shin, D. M., Cancer 94 (2002) 1593-1611). IMC-C225 was also used in clinical trials, including in combination with radiotherapy and chemotherapy (Herbst, R. S., and Shin, D. M., Cancer 94 (2002) 1593-1611). Recently, Abgenix, Inc. (Fremont, Calif.) developed ABX-EGF for cancer therapy. ABX-EGF is a fully human anti-EGFR monoclonal antibody. (Yang, X. D., et al., Crit. Rev. Oncol./Hematol. 38 (2001) 17-23).
So far it was not possible to select antigen binding proteins, in particular antibodies, that specifically bind to the beta-hairpin of HER1 as this beta-hairpin of HER1 represents a hidden epitopes, which is not accessible in the equilibrium state of HER1 (see FIG. 1 and Lemmon, M A, Exp Cell Res. Feb. 15, 2009; 315(4): 638-648)).